Re: [RFC 4/5] RTC: rtc-at91sam9: add device-tree support

[Johan Hovold <jhovold@gmail.com>]

On Mon, Apr 08, 2013 at 12:03:01PM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote:
> On 11:57 Mon 08 Apr     , Nicolas Ferre wrote:
> > On 04/08/2013 11:00 AM, Johan Hovold :
> > > On Mon, Apr 08, 2013 at 09:38:07AM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > >> On 17:12 Sun 07 Apr     , Johan Hovold wrote:

[...]

> > >> the RTT is a general purpose timer backuped that we use in linux as a
> > >> RTC with a gpbr to store the time
> > >>
> > >> you need 2 binding on for the RTT one the RTT-rtc
> > > 
> > > As in adding some virtual hardware-node which uses the rtt and gpbr as
> > > resources?
> > 
> > So, why not simply having a compatibility string that collects the uses
> > of this RTT node:
> > 
> > compatible = "atmel,at91sam9260-rtt-as-rtc", "atmel,at91sam9260-rtt";
> > 
> > And then "decide which device driver to bind to [the RTT] device"...
> > If the rtt-as-rtc driver is not selected, the device can still be used
> > as a simple "rtt". The board .dts can overload a compatibility string
> > according to the use, etc.
> > 
> > Then the way do describe which GPBR to use has still to be discussed.
> > But for the RTT itself, I would keep it simple like that.
> 
> no as infact the rtc-at91sam9 should not even exist
> as this is much more generic
> 
> we use a backped register and a timer to emulate a RTC this can be unsed by
> any one
> 
> and I can use any backuped timer
> 
> we need to have frameworks
> where the gpbr are tracked and the rtt
> 
> 	for you describe the resources
> 
> 	rtt0: rtt@fffffd20 {
> 		compatible = "atmel,at91sam9260-rtt";
> 		reg = <0xfffffd20 0x10>;
> 		interrupts = <1 4 7>;
> 	};
> 
> 	rtc-timer {
> 		compatible = "linux,rtc-timer";
> 		timer = <&rtt0>;
> 		backuped-register = <&gpbr 0>;
> 	};
> 
> this need to SoC implemetation generic

This would indeed be a neat solution, albeit one that requires a lot
work to be realised as both a backup-register and backed-up-timer
framework would need to be implemented.

Thanks,
Johan